CA2926346C

CA2926346C - Method of development of a deposit of high-viscosity oil or bitumen

Info

Publication number: CA2926346C
Application number: CA2926346A
Authority: CA
Inventors: Ravil Rustamovich Ibatullin
Original assignee: Tal Oil Ltd
Current assignee: Tal Oil Ltd
Priority date: 2016-04-07
Filing date: 2016-04-07
Publication date: 2018-11-20
Anticipated expiration: 2036-04-07
Also published as: CA2926346A1

Abstract

The invention relates to methods for the development of heavy oil reservoirs with horizontal wells by thermal recovery The method of heavy oil or bitumen deposits development is carried out by using a pair of horizontal injection and production wells, horizontal sections of which are arranged in parallel one above the other in a productive reservoir. The wells arc equipped with tubing strings that allow simultaneous injection of a heat-transfer agent and production of the fluid. The method includes the steps of injecting the heat-transfer agent, heating the productive reservoir with a steam chamber creation, extracting the fluids by downhole pumps from the lower production well through the tubing strings, the ends of which are located on opposite ends of the horizontal section of the well, measuring mineralization of the produced water, determining the dependence of the steam chamber heating uniformity on the produced water mineralization, and controlling modes the injection of the heat-transfer agent or production of fluids from the wells to achieve a stable value of produced water mineralization to hold a steam chamber heating uniformity. According to the invention, before drilling of the injection and production wells in the appraisal well or during drilling of the said pair of wells, core samples are selected for analyzing water mineralization and determining the composition of dissolved elements. Based on these data, the optimum mineralization is determined to maximize oil recovery from the reservoir After heating up of the reservoir and creating a steam chamber, the mineralization of produced water is determined at least once a day by directly measuring in the stream of the fluid. After reaching a stable value of the produced water mineralization, the injection of the heat-transfer agent in the injection well and the production of the fluids from the production well arc controlled so that the produced water mineralization is held close to the optimum value as much as possible. The method allows increasing oil production and an oil recovery factor by increasing the number of the produced water mineralization measurements and bringing the produced water mineralization to the optimum value.

Description

METHOD OF DEVELOPMENT OF A DEPOSIT OF HIGH - VISCOSITY
OIL OR BITUMEN
The invention relates to the petroleum industry, namely to the methods for developing heavy oil reservoirs using horizontal wells and thermal oil recovery.
Patent RU 2095549 discloses a method of developing heterogeneous oil reservoir, which comprises an alternation of a period of injection of water in the reservoir through an injection well and a simultaneous reservoir fluids extraction through production wells and the period of extraction of the reservoir fluids through the production wells when water is not injected through the injection well. Periodically, once in 2-3 days, produced water is analyzed to determine its mineralization. The injection of water with simultaneous production of the reservoir fluids is carried out to achieve a stable value of the produced water mineralization.
The disadvantages of this method are the high material costs associated with the need to build technological well with two wellheads, the lack of consideration of the initial properties of the produced fluids allowing reaching the highest oil recovery factor, as well as analyzing produced fluids in remote from production locations specialized laboratories, which reduces the reliability of the results.
A method for the development of deposits of heavy oil according to patent RU
2379494 is the closest analog to the present invention. The said method uses a pair of horizontal injection and production wells, horizontal sections of which are arranged in parallel one above :the other in a vertical plane of a producing reservoir. The wells are provided with tubing strings that allow simultaneous downloading of a beat-transfer agent and extracting the fluids, download the heat carrier, heating producing reservoir creating a steam chamber, extracting the fluids by the downhole pumps through the production well through the tubing strings, and controlling technological parameters of the reservoir and the well. The ends of the tubing strings are placed on opposite ends of the horizontal section of the wells. Heating of the producing reservoir starts with steam injection through both wells, heating inter-well reservoir area, reducing the viscosity of heavy oil, and the steam chamber is created by pumping the heat-transfer agent propagating to the top of the producing reservoir with an increase of the steam chamber dimensions. During the extraction of the fluids from time to time (2-3 times a

2 week) mineralization of the produced water is defined, the impact of changes in the produced water mineralization on the steam chamber heating uniformity is determined, and taking into account the changes in produced water mineralization adjust uniformity of the steam chamber heating by controlling the heat carrier injection mode or extraction rate of the production well , to achieve stable value of mineralization of the produced water.
The disadvantages of this method are the lack of consideration of the initial properties of the produced products allowing to reach the highest oil recovery, the implementation of the analysis of produced products in specialized labs, remote from the sampling point, which is produced with large periods (1 every 2-3 days), which reduces the reliability of the results.
The object of the invention is to provide a method, which allows increasing the oil production rate and recovery factor by taking into account the properties of produced fluids, increasing the number of produced water mineralization measurements carried out directly at the well.
This object is achieved by a method of developing deposits of heavy oil or bitumen using a pair of horizontal injection and production wells, horizontal sections of which are arranged in parallel one above the other in a producing reservoir equipped with a tubing string allowing simultaneous injection of a heat-transfer agent and extraction of the product. The method also comprises pumping a heat transfer fluid, heating the producing reservoir with the creation of a steam chamber, extracting the product by the downhole pumps through the lower production well tubing strings, the ends of which arc located on opposite ends of the horizontal section of the well. The mineralization of the produced water is determined, the dependence of the uniformity of the steam chamber heating from the mineralization is determined, and the injection mode of the heat transfer agent and/or the product extraction mode is adjusted to achieve a stable value of mineralization of the produced water ensuring uniform heating of the steam chamber.
According to the invention, before the start of the field development in the appraisal well, or during drilling of the production and injection wells, cores of the producing reservoir arc obtained. The said cores are used for determining water mineralization and composition of the dissolved solids. The optimum produced water mineralization is corresponded to the . . .. .

3 minimum steam-oil ratio and determined for obtaining the maximum oil recovery factor. After the reservoir is heated and the steam chamber is created, the produced water mineralization is determined at least once a day using measuring tools directly in the flow of produced fluids.
After reaching a stable value of produced water mineralization, the heat-transfer agent injection through the injection well and fluid extraction from the production well are adjusted so that the water mineralization approaches optimum level.
Preferably, the measuring devices are located on a substrate of a hydrophilic material.
They are placed at the inlet of the downhole pumps and functionally linked to the appropriate -pumps to 'adjust the product extraction and maintain the lowest possible pressure which is eliminated the gas phase release at the pump intake.
Tle invention is illustrated by the following drawings:
Fig. 1 shows the layout of the wells with one wellhead each;
Fig. 2 shows the layout of the wells with double wellheads;
Fig. 3 is a graph of the coefficient of oil displacement (C(dis) due to mineralization (M) of produced water at Ashalchinskoye field at a temperature of 100 C.
Method of developing deposits of heavy oil or bitumen is implemented as follows.
Before the oil field development in the appraisal well (not shown) or during the drilling production and injection wells 1 and 2 (Figs. 1 and 2) with the horizontal portions 3 and 4 a core of a production reservoir 5 is obtained for the study of the reservoir fluids including water mineralization and composition of dissolved solids. Based on these data, the optimal mineralization of the produced water is determined experimentally in the process of production to obtain the maximum oil recovery factor (CUR) for the reservoir 5. The pair of ' -injectiOn and production wells (Figs. I and 2) is drilled so that their horizontal portions 3 and

4 are arranged in the reservoir 5 in parallel one above the other. The wells I
and 2 can have two wellheads as shown in Fig. I or one wellhead as shown in Fig. 2.
Furthermore, due to individual characteristics of the producing formation, one of the wells may have two wellheads and another one wellhead (not shown in the figures). The wells 1 and 2 are equipped with two corresponding tubing strings 6, 7 and 8, 9.

Instead of tubing strings, the wells 1 and 2 can be fitted with a coil tubing.
The producing wells 2 along the length of its horizontal section 4 can be provided with sensors 10 for additional temperature control. The tubing strings 6 and 7 make it possible to conduct heat transfer agent injection (for example, steam), and tubing strings 8 and 9 to carry out the simultaneous extraction of products with corresponding downhole pumps ii and 12. The reservoir 5 is heated by the steam creating a steam chamber (not shown) above the horizontal part 4 of the production well 2. Due to convective and conductive heat transfer at the stage of development of steam injection in both wells I and 2, the inter-well reservoir zone (zone between the producing well 2 and injecting well 1) is heated reducing the viscosity of the heavy oil. In addition to, oil thermally expands, and, finally, its mobility increases. Then in the process of heavy oil production in the injection well I steam is injected, which is due to the difference in density tends to move to the top of the productive reservoir

5 causing a growth of the steam chamber. On the water-oil interface of the steam chamber and the cold oil and water saturated layer, heat exchange process is constantly going on, in which the steam is condensed into water, and heated heavy oil and associated reservoir water flow to the production well 2 by gravity.
Tubing strings 6, 7 and 8, 9 are arranged in appropriate wells 1 and 2 so as to be able to inject and produce from the opposite ends of the horizontal portions 3 and 4 to enable controlling mineralization of produced water from both ends of the portion 4;
and to enable temperature control along the length of sections 3 and 4 by injecting heat-transfer agent and extracting products by the downhole pumps 11 and 12 to avoid breakthrough of the heat-transfer agent from the injection well I to the production well 2 during extraction of products, and increasing the COR of the reservoir 5.
After heating the reservoir and creating the steam chamber, in the process of extraction , from the production well 2, mineralization of produced water from the well 2 is deterinined not less than once a day directly in the flow of the produced fluids using measuring devices (conventionally not shown), for example, sensors disclosed in documents of RU
2231787, RU
2330272 and others. Measuring devices are arranged in the pipe (not shown) which is transported produced products or for more precise control at the inlets of the downhole pumps 11 and 12. The sensors arc placed on the substrate of a hydrophilic material (for example, silicates and the like) having minimum adhesion to hydrocarbon products of the reservoir 5, which allows obtaining objective measurements through the long period of operation. When installing measuring devices at the inlets of the downhole pumps 11 and 12, or on the wellheads, they are operably linked via a control unit (not shown in the figures) with corresponding downhole pumps 11 or 12 for controlling production by the said pumps and maintaining the lowest possible pressures to eliminate a gas release at an inlet of the corresponding pump 11 and 12 taking into account the mineralization.
Increasing water mineralization raises its boiling temperature since the boiling point of salted water is higher than freshwater one. For example, if the solution contains I% NaC1 (at a pressure of 760 mm Hg, i.e. 101.325 kPa), water has been boiling at 100.21 C; at 2% - 100.42 C;
at 6% -10I.34 C; at 15% - 103.83 C; at 18% - 104,79 C; at 21% - 106.16 C; at 24% -107.27 C; at 27% - 108.43 C; at 29.5% - 109.25 C, etc. For other salts or their combinations, these data can vary. Therefore, the dependence of the water boiling point on water mineralization and pressure is determined for each field after the analysis of the cores obtained while drilling of the reservoir 5. With increasing mineralization, downhole pumps 11 and 12 can operate in a wider range and reduce the pressure at the pump inlet of the pump II or 12 to lower values (to increase efficiency of the pump 11 or 12 to reduce the mineralization) as according to Clausius-Clapeyron equation with increasing pressure, the boiling point increases, and with decreasing pressure, the boiling point decreases respectively.
.1n(7 1 ¨4) = __________________________ - ) cam Mibod. M
wherein Ilia is the boiling point at the inlet of the pump II or 12. K;
P is the pressure at the inlet of the pump 11 or 12, kPa;
. . Pam is the atmospheric pressure (accepted as 101.325 kPa), kPa;
TbuiLatm. is a boiling point at atmospheric pressure, K;
is the specific heat of evaporation, Pkg:
M is molar mass, kgimol;
R is universal gas constant.

6 This relationship is introduced before the operations into the control unit (controller) of the pumps 11 and 12 to prevent vaporization at the downhole pump inlets due to changes in mineralization of produced water.
After achieving equilibrium, the mineralization of water produced by the pumps 11 and 12 of the production well 2 is brought by controlling the heat-transfer agent injection through the tubing strings 6 and 7 in the injection well 1, and the extraction from the production well 2 by pumps 11 and 12 through the tubing strings 8 and 9, with produced water mineralization most approximate to the optimal one determined based on the core study.
The reservoir water mineralization decreases when it is mixed with the steam condensate, and therefore the produced water mineralization has an intermediate value.
There is an equilibrium relationship between the amount of produced oil and the mineralization of the produced water with the subsequent adjustment of the produced volume and steam injection taking into account the optimal mineralization obtained by the core analysis. This process is resulted by steady injection and production. The temperature at the initial stage is controlled in the production well 2 by the temperature sensors 10 to prevent a steam breakthrough in the production well 2. Then a stable value of mineralization is set as õ close as possible to the optimum value without a steam breakthrough to the pumps 11 and 12.
This mineralization is called the equilibrium value of mineralization for the determined fluid temperature. Violation of this balance is indicated by the change in produced water mineralization in samples from the pumps II or 12 while maintaining the fluid temperature. In the process of production, the produced water mineralization is determined, at least once a day, changes in the samples are analyzed, and dependence of the heavy oil production on the produced water mineralization is shown in the figure.
As follows from the graph (Fig. 3), at produced fluid temperature of 100 C
with proper selection of the produced water mineralization, the displacement efficiency approaches the value of 0.7 (70% in a heated zone) taking into account the sweep efficiency factor (Cõ1,v) for steam and gravity action on the reservoir 5 (Figures I and 2) is approximately 0.8 (80% of the reservoir element allocated for a pair of wells 1 and 2) the maximum oil recovery factor (CUR) is equal to 56% according to the formula:
COR = Cvyt - Cohv -100% (2)

7 Thus, the production at the optimal mineralintion of the produced water can significantly increase the COR of the productive reservoir 5.
Increasing mineralization of produced water more than by 10% compared to the equilibrium value of mineralization at predetermined temperature indicates an increase in the reservoir water production in the range of temperature 5-15 C. As a result, the temperature reduction can take place near the production well 2 and interwell zone, which leads to uneven heating of the 'steam -chamber and reducing thermal coverage of the reservoir clement.
Reducing temperature near the production well and inter-well area leads to the increased downhole viscosity of the heavy oil, which in turn reduces oil production and consequently reduces the effectiveness of the thermal recovery in general.
For reducing the mineralization of the produced water and raise the temperature near the production well 2 and in inter-well area and thereby increase the uniformity of heating up of the steam chamber (not shown in figures), it is necessary to increase steam injection through the injection well 1 or to reduce production by respective downhole pumps 11 and/or 12. In this case, the amount of produced water also decreases. With the increase in steam injection volume, the stable heating of all the steam chamber volume increases and stops further reducing the temperature near the production well 2 and inter-well area. In this case, also, the reservoir water is diluted by the discharged condensate, and the mineralization of the produced water is reduced. After recovery uniformity of the heating of the steam chamber, again an equilibrium between the heavy oil production and the produced water mineralization stands taking into account the optimal mineralization at predetermined temperature, but not , . . õ
necessarily at the same level, as evidenced by the graph of dependence of the heavy oil production on the produced water mineralization.
Reduction of the produced water mineralization by more than 10% compared to the equilibrium value also indicates uneven heating of the steam chamber since in such situation there is a premature breakthrough of steam to the production well 2. This leads to unproductive consumption of steam and, therefore, to increase energy costs.
Breakthrough of steam to the production well 2 can also lead to the shutdown of technological equipment due to exposure to high temperatures. In this regard, when mineralization of produced water . . .

8 reduces at a predetermined temperature, it is required to reduce the volume of injected steam or to increase production. With the increase in product withdrawal, the volume of produced cold reservoir water with the increased mineralization also increases, and therefore the mineralization of produced water increases. Since the temperature of the reservoir water, as said above, is about 5T, increasing in its production will reduce the temperature near the production well and in the inter-well area. Increase in production continues until the equilibrium between the amount of extracted heavy oil and mineralization of produced water.
Setup Of equilibrium at a predetermined temperature is judged by the graph of the heavy oil production and the mineralization of produced water.
Increasing the measurement frequency up to I measurement per day (as minimum, the best is online mode) allows to respond more quickly to changes in mineralisation (steam chamber temperature), thus reducing the loss of steam of up to 10% in a breakthrough, eliminate supercooling of the steam chamber that, as a consequence, eliminates the costs up to 15% for an additional heating of the steam chamber caused by these processes and to increase the coverage by the heat exposure.
It is found that the oil production rate (Q..ii, in/day) significantly correlates with the temperature at the wellhead and the total mineralization of the produced water, wherein the flow rate is proportional to the temperature of the produced fluid (T, C), and inversely proportional to the mineralization (M, g/1):
= 0.21 T - 1.38 M -4.33 (3) The correlation coefficient of the model reflects a 79% horizontal well production rate variability. The standard error is equal to 2.6, and its value can be used in setting the . : ,= , , õ.. õ
boundaries of the predictions for new observations.
By controlling the oil production and steam injection volumes, steam/oil ratio (SOR) is evaluated. The said ratio should be maintained at the lowest possible level to reduce the cost of steam:
SOR = Qst.m/Qoil (4) õ . .

9 Monitoring uniformity of heating steam chamber using temperature sensors 10 is disclosed in prior art. However, due to their frequent failures, the effectiveness of the control over the process decreases.
It follows from the foregoing that the method of developing heavy oil deposits allowing carrying out the control of the heat-transfer agent injection and oil production based on the analysis of the produced water mineralization is a very simple and effective way to control the uniformity of the steam chamber heating and increasing the efficiency of the heavy oil recovery.
Examples of specific embodiment Example I.
The Ashalchinskoye heavy oil pilot is located at a depth of 90 m and represented by heterogeneous layers of 20-30 m thick at a temperature of 8 C and pressure of 0.5 MPa. A
pair of horizontal two wellhead wells 1 and 2 (Fig. I) including an injection well 1 and production well 2 were drilled. Corresponding horizontal sections 3 and 4 of the wells were arranged in parallel one above the other in the vertical plane of the production reservoir 5 and equipped with the appropriate tubing strings 6, 7, 8, and 9 configured for simultaneous injection of the heat-transfer agent and production from various ends of the horizontal sections 3 and 4.
The sensors arc installed at the mouth of the outlets of the electrical submersible pumps 11 and 12. They were designed to determine the mineralization of the produced water and arranged on a hydrophilic substrate. During drilling of wells, cores were extracted from õ the productive reservoir 5, said cores showed that the reservoir has oil saturation of 0.70, a porosity of 30%, permeability of 2.65 im2. The oil had a density of 960 kg/m3 and a viscosity of 22000 mPa's, and reservoir water had mineralization of approximately C1õ. =

10 gil.
Mineralization of steam and condensate, respectively, close to zero, i.e., C, << I gil. The mineralization of the produced water may vary in the range from 1 to 10 gil depending on the stage of development of heavy oil reservoir 5. Based on the properties of the reservoir 5, the volume of stream injected into the well 1, temperature and volume of extracted products, it was determined according to formula 3 (based on the experience of operation of such wells of the same deposit) that the greatest amount of extracted oil can be obtained from the reservoir 5 at a temperature of the produced fluid of about 97 C and the optimum mineralization of the produced water of 2A g/l. Before the operation of the horizontal well 2, the inter-well area was heated by simultaneous circulation of steam in each of the wells 1 and 2.
In the process of production of the heavy oil, steam is injected through the injection well I.
Steam extends upwards and creates increasing in size steam chamber. During production mineralization of the produced water is periodically (once a day) determined at the inlets of the pumps 11 and 12. Determined also the dependence of the oil production on mineralization of produced water. At the initial stage of development of the deposit of the heavy oil, an equilibrium is set up between the amount of the heavy oil produced and the mineralization of the produced water at a temperature of about 100 C, which indicates the uniformity of the steam chamber heating. The heavy oil production rate by pumps II and 12 was 12.2 m3/day (SOR
3.7), the mineralization varied in the range of 2.1-2.4 WI.
Equilibrium (average) value of mineralization was 2.2 gil. Extraction by the pumps 11 and 12 was increased to a value that excludes gas release from the produced fluid at the inlet of the pumps 11 and 12 for approaching to the optimum mineralization. Production rate increased to 12.8 m3/day (approximately by 5%), and the mineralization 2.3 gil at the inlets of both pumps

11 and 12 (SOR 3.5). After 34 days of well operation, analysis of mineralization of the produced water at the pump II inlet showed that there was increase in mineralization from 2.3 g/1 to 3.1 g/I, or 34.8%, while the production rate of heavy oil decreased on this pump from 6.4 m3/day to 3 in3/day (total SOR 5.1). This suggests that the increased inflow of cold reservoir water, which helped to reduce the temperature, increasing the mobility of the heavy oil, and reducing the uniformity of beating the steam chamber. The amount of steam injection at that point was 45 m3/day. Based on the analysis, it was decided to increase the volume of steam injection to 55 m3/day for five days. Production by the pump 11 was reduced by half, and by the pump 12 was increased by 10% without a gas release from the fluid at the inlet of this pump by keeping the pressure at the inlet of this pump not less than 100 kPa. The total oil production decreased to 9.8 m3/day (SOR 5.6), rather than up to 6 m3/day (as in similar wells operated by the closest analog). After that in 3 days the mineralization of the produced water at the pump 11 intake began to decline and reached a value of 2.28 g/I, and the production of the heavy oil also increased to 11.3 m3/day (SOR 4.9). The intensity of extraction by the pump 11 was returned to the initial condition, while for the pump 12 it was lowered by 10%. Then, there was stabilization of the heavy oil production at the level of 11.3 m3/day (4% more than in similar wells of the same deposit), and mineralization changed slightly in the range of 2.28-2.4 g/I, which corresponds to the average value of 2.34 g/1 at a temperature of produced fluid ..õ.. equal to 75 C, which close, to the optimal value, which was maintained by production adjustment by the pumps 11 and 12. Later, the temperature increased to 1100 C, while the total production was 13 m3/day (SOR 4.2) with water mineralization of 2.7 g/1 (which is the optimum value for such flow rate and temperature).
After 32 days, mineralization of the produced water increased from 2.7 g/1 to 3.5 2/1 (an increase of 23% at a fluid temperature of 70 C). Average daily production of the heavy oil decreased from 13 m3/day to 10.2 m3/clay (SOR 5.4), which indicated that the steam chamber was cooling. The fluid production was reduced from 100 m3/day to 88 m3/day for aligning the uniform heating of the steam chamber. After that, within 4 days the mineralization of the produced water again began to decline gradually reaching the value of 2.8 g/1, the extraction of the heavy oil at the same time began to increase and stabilized at around

12.9 m'lclay (SOR
4.3) at the product temperature of 100 C. COR was 45%, which is 15% more than that of the closest analog.
Example 2.
On the experimental plot of the Ashalchinskoye heavy oil deposit located at a depth of 90m, represented by heterogeneous layers of 20-30 m thick with a temperature of 8 C. and pressure of 0.5 MPa a pair of horizontal one-wellhead wells 1 and 2 (Fig. 2) was drilled. The said pair consists of an injection well I and a production well 2, corresponding horizontal sections 3 and 4 of which are arranged in parallel one above the other in vertical plane of the producing reservoir 5 and equipped with the appropriate tubing strings 6, 7, 8, and 9 allowing simultaneous injection of a heat- transfer agent and product fluids at different ends of the corresponding horizontal sections 3 and 4. The sensors are installed at the mouth of the outlets of the electrical submersible pumps 11 and 12. They were designed to determine the mineralization of the produced water and arranged on a hydrophilic substrate.
During drilling of the appraisal well (not shown in Fig. 2), cores were produced from the reservoir 5, which showed that the reservoir has oil saturation of 0.70, a porosity of 30%, permeability of 2.65 urn2. The oil had a density of 960 kg/m3 and a viscosity of 22,000 mPa-s, and reservoir water is having a mineralization of approximately Cr, = 10 g/l. Mineralization of steam and condensate respectively is close to zero, i.e. C, << 1 g/I. Mineralization of the produced water may vary in the range from 1 to 10 g/I depending on the stage of development of the heavy oil reservoir 5. Based on the properties of the reservoir 5, the volume of injected steam into the .. well 1, the temperature and the volume of extracted fluids (derived from the operation of such wells of the same deposit), it was found from the formula (2) that the greatest amount of the produced oil from the reservoir 5 would be at the optimum mineralization of the produced water of 3.3 gil. During operation, the equilibrium relationship between the amount of produced heavy oil (13-13,8 m31day) and the volume of the injected steam of 80 m3/day and mineralization of produced water (3,58-3,45 WI) at a temperature of extracted fluids equal to 100 C was achieved. The equilibrium (mean) value of the mineralization was 3.52 However, for such a flow rate, the optimum mineralization was determined based on core analyzes as 3.3 g/l. The production rate was increased at the pumps 11 and 12 by 5%. As a result, the total oil rate was reached 14 m3/day (4% up), and the average produced water mineralization was 3.3 g/1 (SOR 5.7). After 32 days of operation, within three days the mineralization at the inlet of the pump 12 dropped dramatically and reached a value of 2.1 g/l.
The change in mineralization amounted to 33% of the equilibrium value, and the fluid temperature increased to 120 C. This showed that there was a premature breakthrough of steam to the production well 2 resulting in lower exposure of the reservoir, reduction of the uniformity of the steam chamber heating and unproductive use of the heat-transfer agent. For normalizine the mineralization and consequently the temperature near the production well, the production rate by the pump 12 was increased from 43 m3/ day to 49 m3/day. The produced water mineralization normalized in 9 days and reached 3.4 g/l. The values of the fluid production rate by the pumps 11 and 12 were made equal, and the total amount established as

13 97 m3/day, The heavy oil production decreased initially after the steam breakthrough and then stabilized after increasing production rate and remained at 14.2 m3/day (3%
higher than on similar wells) at the temperature of 110 C (SOR 5.6). After three months of operation due to the steam breakthrough, the produced water mineralization at the inlets of both pumps 11 and 12 decreased to 2.1 g/l, and the flow rate of the heavy oil decreased to 11 m3/day at the temperature of fluids at 87 C (SOR 7.3). The steam injection rate was decreased from 80 m3/day to 65 m3/day to restore the balance. The average mineralization at both pumps 11 and 12 increased to a value of 3.3 WI for four days and subsequently remained at this level at a fluid temperature of 90 C. The heavy oil production gradually increased to a value of 14.1 . 10 m3/day.(SOR 4.6). COR_ was 42%, which is 12% higher than that of the closest analog.
The described method of high-viscosity oil or bitumen deposits development by using a pair of horizontal injection and production wells based on the increasing number of the produced water mineralization measurements and approaching of the produced water mineralization to the optimal one determined from the core analysis can increase oil production by 3-5% and recovery factors by 10-15% at comparable values of steam/oil ratio.
,

Claims

14

1. A method of developing reservoir of heavy oil or bitumen using a pair of horizontal injection and production wells having horizontal sections, which are placed parallel one above the other in a productive reservoir, said wells being equipped with tubing strings that allow for simultaneous injection of a heat-transfer agent and extraction of products, said method including the following steps of injecting the heat-transfer agent;
- heating the productive reservoir and creating a steam chamber;
- extract the product by pumps through a lower production well along the tubing strings, the ends of which are located on opposite ends of the horizontal well section;
determining mineralization of the produced water;
determining the dependence of the uniformity of the steam chamber heating on changes of mineralization of the produced water;
- controlling the heat-transfer agent injection or extraction of well products to achieve a stable value of mineralization of the produced water for ensuring uniform heating of the steam chamber; said method characterized in that:
- before drilling wells, in an appraisal well or during the drilling of the wells cores of the productive reservoir are produced;
- the selected cores are used for determining mineralization of the produced water and composition of components dissolved in the water;
- determining the optinium mineralization of produced water corresponding to the minimum steam/bitumen ratio for obtaining maximum oil recovery factor from the reservoir;
- after heating the reservoir and formation of the steam chamber, the mineralization of the produced water is determined at least once a day by measuring devices directly in the flow of the extracted products;
after achieving a stable value of mineralization of the produced water, the injection of the heat-transfer agent in the injection well and the withdrawal of the product from the production well, the injection of the heat-transfer agent in the injection well and extraction of the product through the production well are controlled to avoid a breakthrough of the heat-transfer agent in the production well so that the mineralization of the produced water is as much as possible close to the optimum mineralization.

2. The method according to the claim 1, characterized in that the measuring devices are arranged on a hydrophilic substratemat at the inlets of the pumps, in the wellbore or at the wellhead, and they arc operably linked to the appropriate pump to control the product extraction and to maintain the lowest possible pressure excluding vaporization at the inlet of the pump.